In November 2009, the U.S. EPA published Method 334.0 titled, "Determination of Residual Chlorine in Drinking Water Using an On-Line Chlorine Analyzer" to the Federal Register. While the Method does not specifically endorse any particular chlorine measurement technology, such as amperometric or DPD, it is clearly designed to ensure that the on-line analyzer provides consistently accurate results. Furthermore, it requires that plant personnel be trained in the operation and calibration of the analyzer and are competent in the operation and calibration of the calibration instrument.
It is interesting to note that while the EPA was originally researching the accuracy of amperometric and DPD based on-line chlorine analyzers, they uncovered a bigger concern – regular and proper calibration of these devices. When it comes to chlorine measurements, accuracy is critical to protecting the health and safety of the public. Accurate measurements also have an economic impact as analyzers are required to control the dosing, and therefore consumption of chlorine or chlorine based chemicals.
As stated in Method 334.0, the calibration standards must be NIST (National Institute of Standards and Technology) traceable. For chlorine, titration has been the most common method of calibration. However, titration requires a significant investment in specialized reagents and equipment, and is subject to operator error and interpretation. Titration also requires special skills and procedures, which can be time consuming for those who do not do this regularly. However, a properly trained and experienced person will be able to perform titrations quickly and accurately.
While the Method does provide some general procedures, it does not provide step-by-step instructions for the plant personnel to fulfill the requirements.
Calibration Instrument
Siemens Water Technologies has introduced a new hand-held calibration instrument specifically for on-line chlorine analyzers, providing a simple and reliable solution for compliance with the new Method. The P334 Colorimeter is delivered with a certificate of calibration, which eliminates the need for the operator to verify the calibration curve of a new colorimeter as required by the Method.
The P334's ergonomic, waterproof design makes it ideal for portable or bench top use. Up to 600 tests can be performed before the standard 9-volt battery needs replacement.
Calibrated sample cells and reagent packs simplify sampling. After sample preparation, the free chlorine measurement is displayed within three seconds, and total chlorine measurement takes only three minutes.
The Siemens P334 Colorimeter kit is designed to help operators calibrate on-line chlorine analyzers.
To solve the problems of reading portable instrument displays, the colorimeter has a large backlit display that is clearly visible in all indoor and outdoor lighting conditions, ensuring an accurate recording of the measurements. For added data integrity, 16 measurements can be stored in the colorimeter's memory.
Preparation of primary and secondary standards has been greatly improved and simplified to ensure precise dilution, and requires no special skills or equipment such as Class A Glassware. The liquid standards are contained in double-ended ampoules with a consistent chlorine concentration that eliminates dilution calculations on standards with inconsistent, batch to batch concentrations.
The colorimeter comes with a complete solution procedure to guide plant personnel through each step of the sampling, analysis and calibration procedures outlined in the Method. Also included in the standard kit are a certificate of calibration, sample cells, reagents for up to 100 tests for both free and total chlorine, battery, instruction manual and a carrying case.
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